Types of plate margin There are 2 types of crust: Continental crust which is older, thicker and less dense than… Oceanic crust which is younger, thinner and denser There are 3 directions of movement between plates: Converging: where 2 plates are moving towards each other Diverging: where 2 plates are moving away from each other Passive: where 2 plates are moving side by side There are 6 different combinations of types of crust and directions of movement: Destructive – where oceanic and continental crust converge Destructive – where oceanic and oceanic crust converge Destructive (Collision) – where continental and continental crust converge Constructive – where 2 plates diverge under the ocean Constructive – where continental crust is diverging Conservative – where 2 plates move parallel to each other Each of the 6 combinations above create different tectonic hazards and produce different landforms.

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1. Destructive boundary - Continental / oceanic convergence Description denser oceanic crust is subducted friction and heat cause partial melting of the crust this magma is less dense than the mantle and rises / forces its way through fissures in the lithosphere Landforms deep ocean trenches such as the Peru-Chile trench Fold mountains from rock scraped off the descending plate and folding of the continental crust Hazards Violent volcanoes (composite cone) – due to viscous acidic lavas which block the vents in the volcanoes Powerful earthquakes

Example: South American Plate/Nazca Plate (The Andes)

2. Destructive boundary - Oceanic / oceanic convergence Description 2 plates with oceanic crust collide the densest crust will be subducted Landforms Deep ocean trenches e.g. the Marianas trench Island arcs as volcanoes rise out of the sea e.g. Caribbean, Philippines, Japan, Indonesia Hazards Violent earthquakes and volcanoes

Example: Pacific Plate/North American Plate (Aleutian Islands)

3. Collision boundary - Continental / continental convergence Description Subduction of oceanic crust brings 2 continental masses together Both have a similar density so can’t be subducted Sedimentary rocks scraped off the old sea floor are compressed together to form young fold mountains Landforms Young fold mountains such as the Himalayas (created in the last 40 million years) These are still growing despite erosion Hazards Earthquakes as powerful as at destructive margins

Example: Indian Plate/Eurasian Plate (The Himalayas)

4. Constructive boundary – sub-marine divergence Description plates are moving away from each other causing the crust to weaken and hot magma to force upwards creating a ridge in the centre of the ridge, the crust can subside into to magma below creating a valley the fissures (splits) in the crust provide a route for the more fluid lavas to escape if these continue submarine volcanoes form Landforms Mid-ocean ridges Volcanic islands e.g. Iceland, Surtsey Hazards Volcanoes that erupt with basic (runny) lava – more frequent & less violent eruptions Shallow focus earthquakes

Example: Eurasian/North American (Surtsey)

4. Rifting – continental divergence Description occurs where spreading occurs beneath the continents the up-welling magma leads to fracturing and rifting central sections collapse to form rift valleys volcanoes form where magma forces its way through fissures Landforms Rift valleys such as East African Rift valley – these can widen and eventually get flooded by the sea e.g the Red Sea Volcanoes such as Mt Kilimanjaro & Mt Kenya Hazards Volcanoes Shallow focus earthquakes

Example: African Plate (Great Rift Valley)

4. Conservative boundary – passive movement Description plates are moving parallel to each other, no collision or subduction occurs movement is erratic as plates stick together, pressure builds up and is released in a sudden movement Landforms Fault lines such as the San Andreas and Hayward faults Hazards No volcanoes Earthquakes as powerful as at destructive margins

Example: North American Plate/Pacific Plate (San Andreas Fault)